The invention relates to the field of tissue oximetry systems used for measuring blood oxygenation of in vivo tissue.
The adequate delivery of oxygen to internal organs and tissue is a fundamental requirement for normal biological function, and inadequate delivery can be a sign of pulmonary, cardiac, or vascular complications, all of which require immediate intervention. Despite the importance of tissue oxygenation, the development of clinical technologies for monitoring this parameter has largely stagnated over the last 30 years, and current techniques are limited by their inability to measure key parameters in both the arterial and vascular components, and by the invasive nature of their implementation (e.g. invasive catheters), leading to false diagnoses, late interventions, and infection.
Pulse-oximetry and co-oximetry probes can be found in almost all doctor's offices, intensive care units, surgical suites, endoscopy suites, delivery suites and in most hospital settings. This technology is used to optically monitor arterial oxygen saturation using a simple finger, toe, or ear clip. Adequate tissue oxygenation is necessary for normal organ function and arterial oxygen saturation in a healthy individual is typically between 95-100%. Any decrease below these values (hypoxemia) is cause for immediate intervention, and may indicate inadequate blood oxygenation by the lungs, inadequate blood flow from the heart, or peripheral vasculature problems including shock.
Despite the ubiquity of pulse oximetry, the current technology is incapable of measuring potentially lifesaving information about the oxygen content in the arterial and venous circulation. For example, pulse oximetry cannot measure the quantity or concentration of blood in the peripheral vasculature, which is important for shock differential diagnosis. Pulse oximetry is also incapable of measuring venous oxygen saturation (SvO2) or venous blood concentration, which provides important information related to tissue oxygen extraction, and which currently requires the use of an invasive fiber optic probe catheter in the pulmonary artery, a procedure that carries risk of mechanical damage to the heart and important blood vessels, and infection. New noninvasive and quantitative tissue oxygenation methods are needed to improve patient care at the bedside.